The present invention generally relates to printed circuit board apparatus, and more particularly relates to apparatus and methods for effecting a grounding connection between a printed circuit board and an EMI-shielded housing boss upon which the circuit board is supported.
To provide an EMI-shielded enclosure for electronic equipment, such as printed circuit boards used in computers, plastic housings in which the electronics are operatively disposed are typically plated with a metallic material which is appropriately brought into contact with a grounding structure on the electronics. A low impedance contact between the electronics ground structure and the metallic EMI plating on the housing is required to provide satisfactory EMI shielding of the electronics disposed within the interior of the metal-plated housing.
A printed circuit board in a computer is typically secured within the computer housing by inserting a screw through an appropriate opening in the board and threading the screw into an internally threaded metal insert disposed within an inner end portion of a hollow cylindrical boss projecting inwardly from an exterior wall of the housing. The interior side surface of the housing wall has a metallic EMI plating thereon that extends from the wall along the outer side surface and inner end surface of the boss.
Tightening of the screw into the boss insert is designed to bring the screw head into contact with a grounding pad formed around the circuit board screw opening on one side of the board, and also bring a grounding pad formed around the circuit board screw opening on the other side of the board into contact with the EMI plating material on the inner end of the boss. In this manner, an EMI grounding path is formed from the circuit board grounding pads through the exterior boss plating material to the plating material extending along the inner side of the plastic housing wall from which the integrally molded mounting boss inwardly projects.
In installing the threaded insert within the plated mounting boss before the circuit board is connected thereto, the insert is placed on the inner end of the boss and forcing the boss coaxially into the inner end of the boss while applying heat or ultrasonic vibration to the insert, thereby causing the plastic boss material to "flow" and permit forced insertion of the insert into the boss interior. This forced placement of the insert into the plastic boss interior often disturbs the conductivity of the boss plating, around an outer portion of the boss that receives the insert, due to the lateral expansion of the boss caused by its receipt of the insert. The conductivity disturbance of the boss plating in this outer portion thereof is typically manifested by a cracking of the boss plating which increases the impedence in the EMI shielding conductivity path between the installed circuit board and the EMI plating on the interior side surface of the housing wall from which the boss inwardly projects.
As can readily be seen from the foregoing, it would be highly desirable to provide an improved circuit board-to-housing boss connection structure that essentially eliminates this EMI shielding disturbance problem. It is accordingly an object of the present invention to provide such improved connection structure.